1. Field of the Invention
The present invention relates to a display, and more particularly to a reflective display.
2. Related Art
Various flat panel display devices have been developed to meet the increasingly high requirements for diversified display devices, for example, liquid crystal displays (LCDs), plasma display panels (PDPs), electro-luminescent displays (ELDs), and vacuum fluorescent displays (VFDs). Among the above flat panel display devices, the LCDs have replaced conventional cathode ray tubes (CRTs) to become the dominant products in the market due to the advantages of being light and thin, and having a low power consumption. The LCDs may be approximately categorized into reflective LCDs and transmissive LCDs. The reflective LCD utilizes external light as a light source, and does not need a backlight element, so the reflective LCD consumes less electric power than the transmissive LCD.
A cholesteric LCD is a reflective display using cholesteric liquid crystal to form a liquid crystal layer. The material of the cholesteric liquid crystal may be pure cholesteric liquid crystal, nematic liquid crystal added with a chiral dopant, or nematic liquid crystal added with cholesteric liquid crystal molecules. Generally, the material is mainly a mixed system of the nematic liquid crystal added with a chiral dopant. The mixed system has the advantage that the thermal, optical, and electrical features thereof can be easily modulated. Through a simple molecular design incorporated with a database, cholesteric liquid crystal materials having different reflection wavelengths, liquid crystal phase ranges, and photo-electric features can be obtained quickly depending upon different requirements.
The cholesteric liquid crystal has a bi-stable (memory) effect. Therefore, when no electric field is applied to drive the cholesteric liquid crystal, the displayed image can still remain for a long period of time, so as to save the electric power.
However, the brightness of the reflective display depends on an intensity of the external light source and the light utilization rate of the reflective display, so it is very important to improve the light utilization rate of the display. Furthermore, currently, in most reflective displays, a single pixel includes red (R), green (G), and blue (B) sub-pixels, and each sub-pixel has a different reflectance. Therefore, the effect of true color display is achieved by modulating the brightness of each sub-pixel.